Effect of Intravenous Magnesium on Postoperative Pain and Analgesic Outcomes in Patients Undergoing General Anesthesia: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Intravenous magnesium sulfate has been proposed as an adjuvant analgesic in perioperative care; however, its effects on postoperative pain and related analgesic outcomes remain uncertain. Methods: A systematic search of the literature was conducted from 1 January 2015 through 19 January 2026 to identify randomized controlled trials comparing intravenous magnesium sulfate with placebo in adults undergoing general anesthesia. Pain intensity was harmonized to a 0–10 scale. Primary outcomes were early postoperative pain (0–6 h), pain at 12 h, and pain at 24 h. Secondary outcomes were postoperative opioid consumption, expressed as intravenous morphine equivalents, and time to first rescue analgesia. Random-effects meta-analyses were performed. Risk of bias was assessed using RoB 2, and certainty of evidence using GRADE. Results: A total of 24 randomized controlled trials were included in the qualitative synthesis, of which 22 provided data for quantitative meta-analysis, yielding 23 comparisons and a total of 1750 participants. Intravenous magnesium reduced early postoperative pain (mean difference [MD] −0.90, 95% confidence interval [CI] −1.33 to −0.47; I2 = 96.27%) and pain at 24 h (MD −0.59, 95% CI −1.00 to −0.18; I2 = 66.36%), but not pain at 12 h (MD −0.52, 95% CI −1.15 to 0.11; I2 = 77.38%). Magnesium also reduced postoperative opioid consumption (MD −6.28 mg morphine equivalents, 95% CI −8.94 to −3.61; I2 = 95.93%) and prolonged time to first rescue analgesia (MD 85.61 min, 95% CI 40.11 to 131.10; I2 = 79.37%). Certainty of evidence ranged from very low to moderate, with the highest certainty observed for pain at 24 h. Conclusions: Intravenous magnesium was associated with reduced postoperative pain, particularly at 24 h, and with opioid-sparing effects. However, substantial heterogeneity across outcomes and generally low-to-moderate certainty of evidence warrant cautious interpretation. Magnesium may be considered as part of multimodal analgesia in appropriately selected patients.